In recent years, vehicle window glass has undergone significant evolution in that increasingly dramatic styling changes have brought about the evolution of cylindrically curved door window panes including most recently, doubly curved door window panes.
The introduction of cylindrically curved windows led to significant changes in the window position regulating assemblies, particularly the window guiding system. Typical systems for raising and lowering cylindrical window panels are shown in U.S. Pat. Nos. 2,844,405, 3,808,743, 4,094,100, 4,550,529, 4,730,414 and 4,785,582. Each such U.S. patent shows a vehicle window guiding system comprising at least a single guide channel, and in some instances a pair of guide channels for guiding the raising and lowering of the window pane along a curvlinear path.
With the coming of doubly curved vehicle window panels greater design demands are to be placed on the regulating assemblies for raising and lowering such panels.
The term "doubly curved" refers to a window panel which is not only curved in the direction about the horizontal axis of the vehicle being primarily apparent in the front and rear views of the vehicle, but also curved in the third dimension i.e. about a somewhat vertical axis of the vehicle being primarily apparent in the plan view of the vehicle.
Stated otherwise, a doubly curved window pane is one which is generally convex to the vehicle exterior axis parallel to the centerline of the vehicle and a somewhat vertical axis approximately parallel to the tumblehome in front view of the vehicle. In the truest sense, this invention concerns a window which should be referred to as doubly irregularly curved to provide a truly aerodynamically shaped vehicle. In irregularly curved glass, the degree of convexity of the window is not uniform along any axes. In other words, the rate of curvature is not constant. For example, to produce an aerodynamically advantageous continuous surface, the instantaneous radius of curvature on both the vertical and horizontal sections will be greatest at the upper and forwardmost edges of the window pane.
Were the aforesaid previously known systems to be employed to raise and lower such a window panel, the slot at the belt line of the door through which the window must pass would have to be extremely wide.
In other words, a slot within the door panel at the belt line for passing the window from the fully raised condition to a fully open position must accommodate the depth of the window pane as defined by the degree of convexity as well as the overall uniform cross-sectional thickness of the window pane itself. The task is similar to getting a chair through a doorway. If one were to try and pass a chair straight-on through the doorway, the doorway would have to at least equal the width of the chair. On the other hand, were one to tilt or rotate or pivot the chair as it is passing through the slot defined by the doorway, one could pass a chair of greater width than the width of the doorway. It is upon this general principle that the present invention is based.
An improvement over the aforesaid prior art systems is offered by the system shown in U.S. Pat. No. 4,648,205 wherein the front and rear vertically oriented guide channels are each provided with a different radius of curvature. That is, the front guide channel has a sharper radius of curvature than the rear. Consequently, a cylindrically curved window having a very modest degree of curvature about the somewhat vertical axis of the vehicle can be reasonably accommodated.
However, such a system is not well suited to accommodate a doubly curved window, especially a doubly irregularly curved window having vertical sections along the window where the window curvature is not a radius. The guide channels described in U.S. Pat. No. 4,648,205 do not induce the window to oscillate in plan view side-to-side at different rates at the front and rear as it is raised or lowered, which as explained in detail below is the key to maneuvering a doubly curved cylindrical window panel within a door panel slot of minimum dimension.